High-power solid-state lasers that deliver very high intensity beams for laser machining operations, after being turned on can take up to 5 minutes to reach a stable operating condition. Accordingly during any relatively brief period between operations it is preferable not to turn the laser off. During this period the beam must be terminated, safely, at something other than a work-piece. The beam is terminated at what is usually termed a beam-dump, a beam-terminator or a beam-trap by practitioners of the art. A high-intensity, repetitively pulsed laser beam can reach an average power level from a few hundred (W) to several kilowatts (kW). This makes the design of a beam-terminator very challenging.
Several forms of beam terminators are described in the prior-art. By way of example, U.S. Pat. No. 4,864,098 discloses a beam dump in the form of a cone structure. When such a structure is used with a very high intensity beam, however, the tip of the cone can melt due to a large heat concentration. A simple multiple reflection beam dump arrangement is disclosed in U.S. Pat. No. 5,237,454. This structure arrangement is also susceptible to damage by a high-intensity beam as there is necessarily some beam absorption at each reflection and the first reflection is at near-normal incidence. U.S. Pat. No. 6,792,017 discloses an arrangement wherein a laser beam is trapped by a plurality of absorbing plates in an enclosure through which a cooling fluid is circulated. The beam accesses the enclosure through an optical window. While this arrangement is apparently relatively compact and effective in beam termination, the window could quickly become contaminated in an industrial environment. The contamination would absorb the laser beam which could lead to a run-away absorption condition with a risk of the window breaking and leaking cooling fluid.
It is believed that none of the prior art beam-terminating arrangements is practical for industrial or commercial use with very-high power beams. There is a need for a compact, efficient beam-terminator that has a minimum of operational components and is suitable for use in an industrial environment.